This invention relates to a variable valve timing control apparatus provided in an internal combustion engine (hereinafter referred to as xe2x80x9can enginexe2x80x9d) to change the valve timing of intake valves or exhaust valves, thereby changing operation timing of the intake valves or the exhaust valves in accordance with engine conditions. A variable valve timing control apparatus is proposed in an engine to displace the rotational phase of a camshaft and adjust the valve timing of either an intake valve or an exhaust valve.
This type of apparatus generally is known. For example, relevant related art is disclosed in Japan publication (koukai) No. 10-110603, which is corresponding to a U.S. Pat. No. 5,832,887. This publication discloses a vane-type variable valve timing control apparatus (hereinafter referred to as xe2x80x9cvane-type VTCxe2x80x9d or simply xe2x80x9cVTCxe2x80x9d) which has a housing member rotated by a crankshaft of the engine. The housing has a circular space and fan-shaped spaces protruding from a circumferential surface of the circular space. A vane rotor is accommodated in the housing member and rotates in synchronism with a camshaft. There are plural vanes protruding from the circumferential surface of the vane rotor, each vane is accommodated in each fan-shaped space and defines an advancing hydraulic chamber and a retarding hydraulic chamber. Finally, there is a hydraulic actuating means for actuating hydraulic pressure in the advanced hydraulic chambers and the retarding hydraulic chambers. The hydraulic actuating means selectively supplies the hydraulic fluid to either the advancing hydraulic chambers or retarding hydraulic chambers and discharges the hydraulic fluid from the other of the advancing hydraulic chambers and retarding hydraulic chambers and thereby the vane rotor is rotated relative to the housing.
The publication further describes a locking mechanism for fixing a vane rotor to the housing member. The locking member comprising a locking pin, a spring, and an engaging bore. The locking pin is movably accommodated in a hole provided on the vane. The locking pin has a leading portion provided at one end of the locking pin and a hollow space provided inside of the locking pin. The hollow space has an opening which opens in an opposite direction to the leading head and accommodates the spring. One end of the spring is supported at the bottom surface of the hollow space and the other end is supported at the bottom surface of the hole. Thereby the spring urges the locking pin so that the leading head protrudes from the hole. The engaging bore is provided on the housing member to accommodate the leading head at the most retarding position of the vane rotor with respect to the housing member.
When the engine is out of operation, or when the hydraulic pressure in the retarding hydraulic chambers is under a predetermined value, the vane rotor is at the most retarded position with respect to the housing member and the leading head is urged into an engaging bore by the spring. As a result, an impinging sound that otherwise would be caused by the relative movement of the vanes and the housing member is prevented from being generated even if the camshaft undergoes positive or negative torque variation in driving the intake valves or exhaust valves. When the pressure generated by supplying the hydraulic fluid in the advancing chambers or the retarding chambers becomes over the predetermined value, the leading head of the locking pin is retracted from the engaging bore resisting the spring force and the vane rotor relatively rotates with respect to the housing member.
However, since the spring is accommodated in the hollow space without any support that prevents the spring from buckling, the spring can be buckled undesirably by the movement of the locking pin when the locking pin moves in response to the hydraulic pressure. This causes a clogging of the locking pin in the hole, thus permitting an impinging between the vane and housing member, along with the generation of an undesirable noise.
Accordingly, in view of above-described problems encountered in the related art, a principal object of the present invention is to provide a vane-type VTC that prevents a clogging of the locking pin.
Another object of the present invention is to provide a locking mechanism which is rapidly and reliably movable.
Still another object of the present invention is to provide a vane-type VTC which has an easily assembled locking mechanism.
In order to achieve these and other objects, there is provided a variable valve timing control apparatus for an internal combustion engine, having a first shaft and a second shaft, that comprises a housing member rotated in synchronism with one of the first shaft or the second shaft. The housing has a circular space provided in the housing and at least one fan-shaped space radially extending from an outer circumferential surface of the circular space, a vane rotor rotated in synchronism with the other of the first shaft or the second shaft and accommodated in the housing member in order to relatively rotate with respect to the housing member. The vane rotor has at least one vane radially extending so as to divide each the at least one fan-shaped space into a first chamber and a second chamber. A hole is provided in one of the housing member and the vane, an engaging bore is provided in the other of the housing member and the vane, and a locking mechanism is provided in the hole for fixing the rotational phase between the housing member and the vane rotor that comprises a locking member having a leading head portion provided at the one end of the locking member and a hollow space portion. The hollow space portion has an opening which opens in an opposite direction to that of the leading head portion, a stopper member having a first portion and a second portion, the first portion and the second portion having a different diameter so that a diameter of the second portion is smaller than a diameter of the first portion, the second portion protruding from a side face of the first portion in order that the second portion is accommodated in the hollow space portion. A coil spring is provided between the locking member and the stopper member so as to surround the second portion, the coil spring urging the locking member toward the engaging bore in order that the leading head portion is accommodated in the engaging bore, the locking member being movable in response to hydraulic pressure in the first hydraulic chamber or the second hydraulic chamber in order that the leading head portion is retracted from the engaging bore.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.